1. Field of the Invention
The present invention relates to communications devices and communications systems connected to a device for data transmission/reception and, more specifically, a communications device and a communications system connected to a device and capable of switching a data transmission scheme among nodes.
2. Description of the Background Art
A conventional communications device is described with reference to the drawings. FIG. 8 is a block diagram showing the structure of the conventional communications device. In FIG. 7, a communications device 604 forms one node including a network interface unit 600, a network controller 602, and a CPU (Central Processing Unit) 603.
The network controller 602 transmits/receives data to/from a device 605, such as a CD (Compact Disk) player or a speaker, that is connected to the communications device 604. The network controller 602 also transmits/receives data to/from devices of other nodes through the network interface unit 600. The CPU 603 controls the network controller 602, and communicates with the device 605 and the network controller 602.
The network interface unit 600 is coupled to a network 601, and includes a transmission signal processing unit 606 and a reception signal processing unit 607. The transmission signal processing unit 606 converts data outputted from the network controller 602 into data in a predetermined transmission format appropriate for use over the network 601. The reception signal processing unit 607 converts the data in the transmission format received through the network 601 into data processable by the network controller 602.
FIG. 8 is a block diagram illustrating an exemplary case where six nodes similar in structure to the communications device 604 shown in FIG. 7 are coupled to each other, forming a ring shape network. In FIG. 8, first to sixth nodes 701 to 706 are coupled to each other via the network 601 by each connecting to its adjacent nodes, thereby forming a ring-typed network. Also, the first to sixth nodes 701 to 706 are respectively connected to corresponding first to sixth devices 751 to 756 for communications over the network 601.
In FIG. 8, data outputted from the first device 751 such as a CD player is supplied to the first node 701, and then forwarded to the second node 702 through the network 601. If the destination of the data is not the second node 702, the second node 702 forwards the data to the third node 703. In this manner, the data is transferred clockwise until it reaches the destination.
Consider a case, for example, where the third device 753 is a right speaker and the fifth device 755 is a left speaker. In this case, right and left audio data outputted from the first device 751 such as a CD player is forwarded, through the first node 701 and the second node 702, to the third node 703. In the third node 703, audio data for the right speaker is extracted, and then forwarded to the third device 753. The right and left audio data is further forwarded through the fourth node 704 to the fifth node 705. In the fifth node 705, audio data for the left speaker is extracted, and then forwarded to the fifth device 755.
Here, in the communications device 604 shown in FIG. 7, the transmission signal processing unit 606 and the reception signal processing unit 607 each require some time for processing signals. Also, the network controller 602 requires some processing time. Furthermore, communications with the device 605 requires a predetermined time. Therefore, if the first to sixth nodes 701 to 706 similar in structure to the device 604 are coupled in a ring shape as shown in FIG. 8, a time lag occurs between the time when data outputted from the first node 701 reaches the third node 702 and the time when the data reaches the fifth node 705.
More specifically, if the output data from the first node 701 is digital stereo audio data, a time lag occurs between the time when right audio data reaches the third device 753 and the time when left audio data reaches the fifth device 755. As a result, right audio and left audio are reproduced with a time lag, sounding strange to listeners. This also occurs in the case of three or more speakers, even more than in the case of two speakers.
To reduce such time lag, a predetermined delay is applied to the device (or node) side which data should reach earlier. However, if the lag varies with changes of the data transmission scheme or other factors, the predetermined fixed delay cannot be used.
Therefore, an object of the present invention is to provide a communications system and a communications device that can accurately correct, with a simple structure, a delay to be applied in order to reduce the difference in reaching time of data that should simultaneously reach respective destinations, thereby providing audio reproduction without making listeners feel strange.
The present invention has the following features to attain the object above.
A first aspect of the present invention is directed to a communications system comprising a plurality of nodes including at least one transmission scheme variable node that selects a transmission scheme for use from a plurality of transmission schemes, and a network coupling the transmission nodes, wherein
the transmission scheme variable node carries out communications for transmitting, before using the selected transmission scheme, information about the selected transmission scheme to another node by using a previously set transmission scheme, thereby correcting reaching times of data that should almost simultaneously reach respective two or more different nodes.
As described above, in the first aspect, it is possible, with a simple structure, to accurately correct a delay to be applied in order to reduce the difference in reaching time of data that should simultaneously reach respective destinations, such as data for the right speaker and data for the left speaker. Thus, a communications system capable of reproducing audio without making listeners feel strange.
According to a second aspect, in the first aspect,
the transmission scheme variable node includes
a network controller for communicating with a device externally provided, and controlling data communications with the other node;
a central processing unit for controlling the network controller for communications;
a transmission signal processing unit for converting data coming from the network controller into a transmission signal over the network;
a reception signal processing unit for converting a reception signal received over the network into data processable by the network controller;
a transmission scheme determination part for selecting the transmission scheme for use in the transmission signal processing unit and reporting information about the selected transmission scheme to the other node, and setting the transmission scheme for use in the transmission signal processing unit and the reception signal processing unit; and
a switching unit for switching, after the information about the transmission scheme selected by the transmission scheme determination part is transmitted to the other node, connection of the transmission signal processing unit and the reception signal processing unit to the network.
As described above, in the second aspect, even if the transmission scheme is changed in each node, the information about the transmission scheme for use is transmitted to another node, thereby accurately correcting the delay to be applied in order to reduce the difference in reaching time of data that should simultaneously reach respective destinations.
According to a third aspect, in the second aspect,
the central processing unit receives the information about the transmission scheme selected by the transmission scheme determination part, and calculates a delay time for correcting the reaching time of the data.
As described above, in the third aspect, only with transmission of the information about the transmission scheme, the delay time can be correctly calculated by the central processing unit.
A fourth aspect is directed to a communications device for carrying out communications for transmitting, before using a transmission scheme selected from a plurality of transmission schemes, information about the selected transmission scheme to another node by using a previously set transmission scheme, thereby correcting reaching times of data that should almost simultaneously reach respective two or more different nodes coupled to each other via a network, and the communications device includes:
a network controller for communicating with a device externally provided, and controlling data communications with the other node;
a central processing unit for controlling the network controller for communications;
a transmission signal processing unit for converting data coming from the network controller into a transmission signal over the network;
a reception signal processing unit for converting a reception signal received over the network into data processable by the network controller;
a transmission scheme determination part for selecting a transmission scheme for use in the transmission signal processing unit and reporting information about the selected transmission scheme to the other node, and setting the transmission scheme for use in the transmission signal processing unit and the reception signal processing unit; and
a switching unit for switching, after the information about the transmission scheme selected by the transmission scheme determination part is transmitted to the other node, connection of the transmission signal processing unit and the reception signal processing unit to the network.
As described above, in the fourth aspect, even if the transmission scheme is changed in each node, the information about the transmission scheme for use is transmitted to another node, thereby accurately correcting the delay to be applied in order to reduce the difference in reaching time of data that should simultaneously reach respective destinations.
According to a fifth aspect, in the fourth aspect,
the central processing unit receives the information about the transmission scheme selected by the transmission scheme determination part, and calculates a delay time for correcting the reaching time of the data.
As described above, in the fifth aspect, only with transmission of the information about the transmission scheme, the delay time can be correctly calculated by the central processing unit.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.